Toner-density calculating method, reflective optical sensor, reflective optical sensor device, and image forming apparatus

ABSTRACT

A toner density is calculated from outputs of light-receiving elements based on a difference between a reflection property of a supporting member and a reflection property of a toner pattern. Light-emitting elements aligned in one direction that is inclined to a sub-direction emit a detection light in such a manner that a distance between adjacent spots falling on the supporting member in a second direction is equal to or smaller than a width of the toner pattern in the second direction. The light-receiving elements receive a reflected light reflected from the supporting member and/or the toner pattern. The light-receiving elements are aligned, opposed to the supporting member, in a one direction corresponding to the light-emitting elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/399,356, filed on Mar. 6, 2009 now U.S. Pat. No. 8,260,164, theentire disclosure of which is incorporated herein by reference thereto,and incorporates by reference the entire contents of Japanese prioritydocument 2008-070198, filed in Japan on Mar. 18, 2008, and Japanesepriority document 2008-238451, filed in Japan on Sep. 17, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technology for calculating a tonerdensity.

2. Description of the Related Art

A variety of image forming apparatuses use toner to form images, i.e.,they form toner images. Example of such image forming apparatuses areanalog image forming apparatuses, digital image forming apparatuses,black-and-white copiers, color copiers, printers, plotters, facsimilemachines, and, multifunction printers (MFPs).

To form a good quality toner image, as is widely known, an electrostaticlatent image needs to be developed with just an appropriate amount oftoner. The electrostatic latent image can be developed with atwo-component developer that contains toner and carrier or asingle-component developer that contains only toner. An amount of thetoner to be supplied to a developing unit that develops theelectrostatic latent image is called, hereinafter, “toner density”.

If the toner density is low, i.e., if the amount of the toner suppliedto the electrostatic latent image is less than the necessary amount, apaler toner image will be formed. If the toner density is high, i.e., ifthe amount of the toner supplied to the electrostatic latent image ismore than the necessary amount, a darker and difficult-to-see tonerimage will be formed. To form a good quality toner image, the tonerdensity should be within an appropriate range.

To adjust the toner density to a value within the appropriate range, itis necessary to measure the current toner density. In a typical method,the toner density is measured from a change in a detection lightreflected from a toner image that is formed dedicated to thetoner-density measurement (hereinafter, “toner pattern”). An opticaldevice that emits the detection light to the toner pattern and receivesthe detection light reflected from the toner pattern is called areflective optical sensor.

Various types of reflective optical sensors are known in the art (seeJapanese Patent Application Laid-open No. S64-35466, Japanese PatentApplication Laid-open No. 2004-309292, Japanese Patent ApplicationLaid-open No. 2004-21164, and Japanese Patent Application Laid-open No.2002-72612).

Typical reflective optical sensors include a light-emitting unit and alight-receiving unit. The light emitting unit includes one, two, orthree light-emitting elements having different wavelengthcharacteristics. The light-receiving unit includes one or twolight-receiving elements (e.g., photodiodes (PDs) or phototransistors).

Light-emitting diodes (LEDs)) are typically used as the light-emittingelements. The LEDs emits the detection light of a spot size that issmaller than the toner pattern on the toner pattern.

The toner pattern is formed, for example, on a transfer belt. The tonerpattern moves as the transfer belt rotates. A direction in which thetransfer belt moves due to the rotation is called a sub-direction, and adirection perpendicular to the sub-direction is called a main-direction.In a system in which electrostatic latent images are formed throughoptical scanning, the main-direction corresponds to the main-scanningdirection, and the sub-direction corresponds to the sub-scanningdirection.

An electrostatic latent image corresponding to a toner pattern is formedon a photosensitive member by optically scanning a surface of thephotosensitive member with an electrostatic-latent-image forming unit,and the electrostatic latent image on the surface of the photosensitivemember is then developed into the toner pattern. The toner pattern onthe photosensitive member is then transferred onto the transfer belt,and is moved in the sub-direction with the rotation of the transferbelt. When the toner pattern enters a detection area, the toner patternis exposed with a spot of the detection light from the reflectiveoptical sensor. The spot size of the spot of the detection light istypically about 2 millimeters (mm) to 3 mm.

In an ideal situation, the spot falls on the center of the toner patternin the main-direction. However, it is difficult to always keep arelative position between the toner pattern and the reflective opticalsensor in the main-direction the ideal state, due to various reasons.These reasons include fluctuation in an optical scanning area of theelectrostatic-latent-image forming unit, meandering of the transferbelt, positional shift of the reflective optical sensor in themain-direction from an initial installation position because of passageof time.

If a portion of the spot falls in a region where there is no tonerpattern because of the positional miss-match in the main-directionbetween the toner pattern and the reflective optical sensor, thereflected light received by the light-receiving unit represents wrongdata, and therefore the measured toner density is wrong. Assume, forexample, that one light-emitting element emits one spot of the detectionlight, one light-receiving element receives the reflected light, and thetoner density is calculated from a difference between a specularreflection light and a diffuse reflection light. The light-receivingelement is arranged to receive the specular reflection light. If a firstportion of the spot falls in a region where there is no toner patternand a second portion falls on the toner pattern, the first portion ofthe detection light is reflected specularly while the second portion isreflected diffusely. As a result, in a configuration where thelight-receiving element is arranged so as to receive the specularreflection light, as compared to a case where the entire spot falls outof the toner pattern, intensity of the specular reflection light that isreceived at the light-receiving element decreases due to the generationof the diffuse reflection light. The decrease in the intensity of thespecular reflection light can also occur when the toner amount at thetoner pattern is low. Therefore, the decrease in the intensity of thespecular reflection light is due to low toner amount or miss-matchbetween the spot and the toner pattern is always unclear.

To solve this problem, in the conventional techniques, the toner patternof a size from about 15 mm to about 25 mm in both the main-direction andthe sub-direction is formed so that the spot of the detection lightcannot fall out of the toner pattern even in case of the positionalmiss-match.

In the image forming apparatuses, specifically, the color image formingapparatus, the measurement of the toner density by the reflectiveoptical sensor using the toner pattern is performed to acquire andmaintain high image quality as a maintenance activity necessary for anaccurate image-forming process. Because the toner-density measurement isperformed as the maintenance activity separated from the main activity,i.e., an image-forming process, the image formation cannot be performedduring the toner-density measurement.

When the electrostatic latent image to be developed to the toner patternis written by the optical scanning, time required for the opticalscanning is in proportion to the size of the toner pattern. In otherwords, the larger the toner pattern is, the lower the operatingefficiency of the image formation becomes.

Moreover, because a total amount of the toner in the toner container orthe like is fixed, as an amount of the toner to be used for the tonerpattern increases, an amount of the toner to be used for the mainactivity, i.e., the image formation decreases, disadvantageously. Thelarger the toner pattern is, the more the toner is consumed for thetoner pattern. In this manner, the conventional toner-density measuringmethods have the two disadvantages, i.e., the low operating efficiencyand the large toner-consumption amount for the toner pattern.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to an aspect of the present invention, there is provided atoner-density calculating method implemented on a toner image formingapparatus. The toner-density calculating method includes forming apredetermined toner pattern on a surface of a supporting member thatmoves in a first direction; emitting a detection light onto thesupporting member with a light-emitting unit; receiving a reflectedlight reflected from at least one of the supporting member and the tonerpattern with a light-receiving unit; and calculating a toner density ofthe toner pattern based on a difference between a reflection property ofthe supporting member to the detection light and a reflection propertyof the toner pattern to the detection light. The light-emitting unitincludes M number of light-emitting elements aligned in a thirddirection that is inclined to the first direction, where M is equal toor larger than three, wherein the light-emitting elements emit thedetection light so that M number of light spots fall on the supportingmember in such a manner that a distance between adjacent light spots ina second direction that is perpendicular to the first direction in aplane of the supporting member is equal to or smaller than a width ofthe toner pattern in the second direction, the light-receiving unitincludes N number of light-receiving elements that receive the reflectedlight from at least one of the supporting member and the toner pattern,where N is equal to or larger than three, wherein the light-receivingelements are aligned, opposed to the supporting member, in a singledirection, corresponding to the light-emitting unit, and the calculatingincludes calculating the toner density from outputs of thelight-receiving elements.

According to another aspect of the present invention, there is provideda reflective optical sensor for use in a toner image forming apparatus.The reflective optical sensor includes a light-emitting unit that emitsa detection light onto a supporting member that moves in a firstdirection, the light-emitting unit including M number of light-emittingelements aligned in a fourth direction, where M is equal to or largerthan three, the light-emitting elements turning ON/OFF individually orsimultaneously; and a light-receiving unit that receives a reflectedlight reflected from at least one of the supporting member and a tonerpattern formed on the supporting member, the light-receiving unitincluding N number of light-receiving elements aligned in a fifthdirection corresponding to the light-emitting unit, where N is equal toor larger than three.

According to still another aspect of the present invention, there isprovided a toner-density calculating method implemented on a toner imageforming apparatus. The toner-density calculating method includes forminga predetermined toner pattern on a surface of a supporting member thatmoves in a first direction; emitting a detection light onto thesupporting member with a light-emitting unit; receiving a reflectedlight reflected from at least one of the supporting member and the tonerpattern with a light-receiving unit; and calculating a toner density ofthe toner pattern based on a difference between a reflection property ofthe supporting member to the detection light and a reflection propertyof the toner pattern to the detection light. The light-emitting unitincludes M number of light-emitting elements aligned in a thirddirection that is inclined to the first direction, where M is equal toor larger than three, the light-emitting elements emit the detectionlight so that M number of light spots fall on the supporting member insuch a manner that a distance between adjacent light spots in a seconddirection that is perpendicular to the first direction in a plane of thesupporting member is equal to or smaller than a width of the tonerpattern in the second direction, the light-receiving unit includes Nnumber of light-receiving elements that receive the reflected lightreflected from at least one of the supporting member and the tonerpattern, where N is equal to or larger than three, the light-receivingelements are aligned, opposed to the supporting member, in a singledirection, corresponding to the light-emitting unit, the emittingincludes emitting the detection light sequentially from the Mlight-emitting elements. The calculating includes when a firstlight-emitting element emits the detection light, categorizing an outputof a first light-receiving element corresponding to the firstlight-emitting element to a specular reflection output representingspecular reflection light, and categorizing outputs of non-correspondinglight-receiving elements to the first light-emitting element to diffusereflection outputs representing diffuse reflection light; andcalculating the toner density based on categorized outputs of thelight-receiving elements.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an image forming apparatus according toa first embodiment of the present invention;

FIG. 2 is a schematic diagram for explaining toner-pattern detectionperformed by a reflective optical sensor illustrated in FIG. 1;

FIGS. 3A to 3F are schematic diagrams for explaining the toner-patterndetection by the reflective optical sensor;

FIG. 4A is a schematic diagram of an arrangement of light-emittingelements and light-receiving in a reflective optical sensor according toa second embodiment of the present invention;

FIG. 4B is a schematic diagram of an arrangement of light-emittingelements and light-receiving in a reflective optical sensor according toa third embodiment of the present invention;

FIG. 5 is a schematic diagram of an arrangement of light-emittingelements and light-receiving in a reflective optical sensor according toa fourth embodiment of the present invention;

FIG. 6A is a schematic diagram of an arrangement of light-emittingelements and light-receiving in a reflective optical sensor according toa fifth embodiment of the present invention;

FIG. 6B is a schematic diagram of an arrangement of light-emittingelements and light-receiving in a reflective optical sensor according toa sixth embodiment of the present invention;

FIG. 6C is a schematic diagram of an arrangement of light-emittingelements and light-receiving in a reflective optical sensor according toa seventh embodiment of the present invention;

FIG. 7A is a schematic diagram of a reflective optical sensor accordingto an eighth embodiment of the present invention;

FIG. 7B is a schematic diagram of a reflective optical sensor accordingto a ninth embodiment of the present invention;

FIGS. 8A to 8C are schematic diagrams of a reflective optical sensoraccording to a tenth embodiment of the present invention

FIGS. 9A and 9B are schematic diagrams of a reflective optical sensoraccording to an eleventh embodiment of the present invention;

FIG. 10A is a schematic diagram of a reflective optical sensor accordingto a twelfth embodiment of the present invention;

FIG. 10B is a schematic diagram of a reflective optical sensor accordingto a thirteenth embodiment of the present invention;

FIGS. 11A to 13C are bar charts for explaining a toner-density measuringmethod according to a fourteenth embodiment of the present invention;and

FIG. 14 is a schematic diagram of a reflective optical sensor deviceaccording to a fifteenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described in detailbelow with reference to the accompanying drawings.

The method of forming images with toner is used in the copiers, theprinters, the plotters, the facsimile machines, the MFPs, etc. Themethod of forming images with toner includes the process of forming theelectrostatic latent image and the process of developing theelectrostatic latent image to the toner image. The process of formingthe electrostatic latent image is, more particularly, the process ofexposing a photoconductive latent-image carrier with an evenly-chargedsurface to a light by the optical scanner or the like.

The toner pattern is a toner image for the toner-density measurement.The toner pattern is formed by developing a predetermined electrostaticlatent image. The toner pattern is on a supporting member in themeasurement. In other words, the toner pattern is formed on thesupporting member and then is moved in the sub-direction to thedetection area.

The electrostatic latent image to be developed to the toner pattern canbe formed by exposure of an image with a pattern having a predetermineddensity or by writing by the optical scanning.

As described above, the supporting member moves, in the toner-densitymeasurement, in the sub-direction, carrying the toner pattern thereon.The supporting member can be, for example, a latent-image carrier onwhich the electrostatic latent image is formed and a transfer belt or anintermediate transfer belt that is used to transfer the toner image.

In the following description, “predetermined toner pattern” means that ashape of the toner pattern is fixed. Moreover, “single directionintersecting the sub-direction” includes the direction perpendicular tothe sub-direction, i.e., the main-direction. “Distance between adjacentspots in a direction perpendicular to the sub-direction” means adistance between adjacent ones of spots formed on the surface of thesupporting member aligned in the single direction perpendicular to thesub-direction, i.e., the main-direction when each of M-number of thelight-emitting elements emits the detection light. Moreover, “distancebetween adjacent spots” means not a distance between centers of theadjacent spots in the main-direction but, if the adjacent spots are notoverlapped with each other, a distance between circumferences of theadjacent spots in the main-direction.

Specifically, it is assumed in the following description that M-numberof the light-emitting elements are aligned in the main-direction at a3-mm pitch, and the diameter of the circular spots is 2 mm. In otherwords, the distance between adjacent spots is 1 mm in themain-direction. This 1-mm interval between the adjacent spots is notexposed to the detection light.

However, if the toner pattern is larger than the distance between theadjacent spots (1 mm) in the main-direction, at least a part of thetoner pattern is exposed to any of the spots when the toner patternpasses through an area on which the spots are aligned. Therefore, it isenough for the toner pattern to be a little larger than 1 mm in themain-direction to be exposed to the spots of the detection light. Inother words, a toner pattern that is much smaller than the conventionaltoner pattern (15 mm to 25 mm) in width in the main-direction issufficient.

The distance between the adjacent spots in the direction perpendicularto the sub-direction should be set smaller than the width of the tonerpattern in the main-direction. That is, the distance between theadjacent spots can be smaller than 1 mm, and, moreover, the adjacentspots can have an overlap in the main-direction. If the adjacent spotsare overlapped, the distance between adjacent spots is a minus value,and the areas that are exposed to the spots of the detection light makea single area continuous in the main-direction. Therefore, the width ofthe toner pattern in the main-direction can be decreased infinitely, inprincipal.

Moreover, even if the spot size is smaller than the width of the tonerpattern in the main-direction, it is possible to expose without fail thetoner pattern to the detection light by adjusting the pitch between theadjacent spots in the main-direction to a value smaller than the widthof the toner pattern in the main-direction. This is because, by theadjustment, the distance between the adjacent spots in themain-direction becomes smaller than the width of the toner pattern inthe main-direction.

When the light-emitting unit emits the detection light to the supportingmember, the detection light is reflected from the surface of thesupporting member and/or the toner pattern, and is received by thelight-receiving unit. The light-receiving unit includes three or morelight-receiving elements. The intensity of the light received at each ofthe light-receiving elements varies depending on a positional relationbetween the spots of the detection lights and the toner pattern. Thetoner density is measured accurately from outputs of the three or morelight-receiving elements.

As is widely known, when the detection light strikes the toner pattern,the detection light is diffusely reflected. On the other hand, if thesurface of the supporting member is specular and when the detectionlight strikes an area out of the toner pattern on a surface of thesupporting member, the detection light is specularly reflected. Thesupporting member can be, for example, a photoconductive latent-imagecarrier.

Accordingly, the reflection property when the detection light strikesthe area out of the toner pattern on the surface of the supportingmember shows the specular reflection, while the reflection property whenthe detection light strikes the toner pattern shows the diffusereflection. The difference in the reflection properties causes avariation of the intensities of the light received at the three or morelight-receiving elements. Therefore, a degree of the toner darkness(i.e., the toner density) can be measured from outputs of the three ormore light-receiving elements.

If a transfer belt or an intermediate transfer belt is used as thesupporting member, the surface of the supporting member reflects, insome cases, the detection light substantially specularly almost as amirror surface reflects, and reflects, in other cases, the detectionlight diffusely. Even in a case that the surface of the supportingmember reflects the detection light diffusely, if there is a differencebetween the diffuse reflection from the area out of the toner patternand the diffuse reflection from the toner pattern, a distribution of theintensities of the light received at the plural light-receiving elementswhen the detection light is diffusely reflected from the area out of thetoner pattern differs from the distribution when the detection light isdiffusely reflected from the toner pattern. Therefore, the toner densitycan be measured correctly.

In the following description, it is assumed that both M, which is thenumber of the light-emitting elements that form the light-emitting unit,and N, which is the number of the light-receiving elements that form thelight-emitting unit, are equal to or larger than three. It is allowableto set M equal to N (M=N) or different from N (M≠N). Moreover, it isallowable to set M larger than N (M>N) or M smaller than N (N<M).

Three or more LEDs aligned in a single direction can be used as thelight-emitting elements of the light-emitting unit. If the LEDs have alens function of collecting divergent light, the LEDs are arranged insuch a manner that the detection light forms the sport with a desiredsize on the supporting member.

Alternatively, an LED array including three or more light-emittingelements can be used as the light-emitting unit. In this case, alight-collection optical system can be included in the light-emittingunit to collect the light emitted from the LED array.

PDs can be used as the light-receiving elements of the light-receivingunit. Alternatively, a PD array including three or more PDs (e.g.,charge-coupled device (CCD) line sensor) can be used as thelight-receiving unit.

The lower limit of M or N is, as described above, three. The upper limitof M or N is determined appropriately based on the practical size of thereflective optical sensor for the toner-density measurement. The upperlimit of M is, preferably, about 500. The upper limit of N can beseveral thousands as large as the number of PDs in the above-describedPD array.

The light-emitting elements in total of M can be tuned ON/OFF in variousmanners. For example, all the light-emitting elements turn ON/OFF,simultaneously. Alternatively, the light-emitting elements turn ON/OFF,sequentially one after another. Still alternatively, the light-emittingelements are categorized into several groups. For example, even-numbergroups and odd-number groups are arranged alternately. Thelight-emitting elements turn ON/OFF sequentially on the group basis froma group arranged on an end.

M is equal to P·m. The light-emitting unit includes P-number of groupseach including m-number of light-emitting elements. A firstlight-emitting element of each group turns ON/OFF, i.e., the firstlight-emitting elements in total of P turn ON/OFF, simultaneously. Afterthat, a second light-emitting element of each group turns ON/OFF, i.e.,the second light-emitting elements in total of P turn ON/OFF,simultaneously. This ON/OFF operation is repeated until m-thlight-emitting element of each group turns ON/OFF.

The toner pattern is a toner image having a fixed shape that is formedto measure the toner density. The toner pattern can be, for example, ahomogenous toner image representing a reference density. The imageforming apparatus determines whether the toner density is higher thanthe reference density based on degree of the darkness of the tonerimage. Alternatively, as described later, the toner pattern can be acollection of toner images each representing different referencedensities. Although each of the toner images is the toner pattern, thecollection of the toner images can be called “toner pattern”. Stillalternatively, the different toner images form a single pattern. Inother words, this single pattern is a gradation image having varioustoner densities gradually changed.

The light-emitting unit includes M-number of the light-emittingelements, where M≧3, aligned in a single direction. The light-emittingelements turn ON/OFF individually or simultaneously.

The light-receiving unit includes N-number of the light-receivingelements, where N≧3, aligned in a single direction corresponding to thelight-emitting unit.

The light-emitting unit can include M-number of individual LEDs as thelight-emitting elements. Alternatively, the light-emitting unit can be,for example, an LED array including M-number of LEDs. Thelight-receiving unit can include N-number of individual PDs as thelight-receiving elements. Alternatively, the light-receiving unit canbe, for example, a PD array including N-number of PDs.

In the following description “the light-emitting elements and thelight-receiving elements are aligned in a single direction” includes notonly the light-emitting elements and the light-receiving elementsaligned in one line extending in the single direction but also thelight-emitting elements and the light-receiving elements aligned inseveral parallel lines extending in the single direction. The severallines on which the light-emitting elements and the light-receivingelements are aligned are, of course, parallel to or intersecting themain-direction. The several lines are parallel to each other.

Image forming apparatuses can perform a toner-density measurement methodaccording to any of embodiments of the present invention by using thereflective optical sensor.

If the number of the light-receiving elements non-corresponding to acertain one of the light-emitting elements is N−3 or N−2, the number ofthe light-emitting elements (M) is equal to the number of thelight-receiving elements (N), i.e., the light-emitting elements arecorresponding to the light-receiving elements in a one-to-one manner.When the certain light-emitting element is arranged other than bothends, the number of the non-corresponding light-receiving elements isN−3. When the certain light-emitting element is arranged on an end, thenumber of the non-corresponding light-receiving elements is N−2. Inanother case, the number of the non-corresponding light-receivingelements is N−(2n+1), when the certain light-emitting element isarranged other than both ends; and is N−2n when the certainlight-emitting element is arranged on an end, where n is a naturalnumber.

An image forming apparatus according to a first embodiment of thepresent invention is described with reference to FIG. 1.

The image forming apparatus illustrated in FIG. 1 is a color imageforming apparatus; however, the following description will apply even toa monochrome image forming apparatus. A color image is formed with fourtoners including yellow (Y), magenta (M), cyan (C), and black (K).

The image forming apparatus includes an optical scanning device 20. Theoptical scanning device 20 can be any widely-known scanner.

The image forming apparatus includes drum-shaped photosensitive elements11Y, 11M, 11C, and 11K as photoconductive latent-image carriers. Thephotosensitive element 11Y is used for forming a yellow toner image, thephotosensitive element 11M is for a magenta toner image, thephotosensitive element 11C is for a cyan toner image, and thephotosensitive element 11K is for a black toner image.

The optical scanning device 20 writes images onto the photosensitiveelements 11Y, 11M, 11C, and 11K by the optical scanning. Thephotosensitive elements 11Y, 11M, 11C, and 11K are rotated in aclockwise direction at a constant speed, charged evenly by chargingrollers TY, TM, TC, and TK as charging units, and scanned by the opticalscanning device 20. Thus, electrostatic latent images (negative latentimages) for yellow, magenta, cyan, and black are written onto thephotosensitive elements 11Y, 11M, 11C, and 11K, respectively.

Those electrostatic latent images are developed by developing devicesGY, GM, GC, and GK, and thus the yellow toner image, the magenta tonerimage, the cyan toner image, and the black toner image are formed on thephotosensitive elements 11Y, 11M, 11C, and 11K, respectively as positiveimages.

The toner images are transferred onto a recording sheet (not shown)(e.g., transfer paper and plastic sheet for overhead projector) via atransfer belt 17.

The recording sheet is conveyed from a sheet table (not shown) that isarranged under the transfer belt 17 to an upper-right circumference ofthe transfer belt 17 illustrated in FIG. 1. After that, the recordingsheet is attached to the transfer belt 17 by the exertion of theelectrostatic force, and is conveyed to the left side of FIG. 1 bycounterclockwise rotation of the transfer belt 17. The recording sheetsequentially receives, while being conveyed, the yellow toner image fromthe photosensitive element 11Y by a transfer member 15Y, the magentatoner image from the photosensitive element 11M by a transfer member15M, the cyan toner image from the photosensitive element 11C by atransfer member 15C, and the black toner image from the photosensitiveelement 11K by a transfer member 15K.

In this manner, a full-color image is formed on the recording sheet in asuperimposed manner. After that, the full-color image is fixed onto therecording sheet by a fixing device 19. The recording sheet with thefull-color image is discharged out of the image forming apparatus. Thefull-color image can be formed onto an intermediate transfer belt in thesuperimposed manner and then transferred from the intermediate transferbelt to the recording sheet, instead of directly being formed on therecording sheet.

The image forming apparatus illustrated in FIG. 1 includes reflectiveoptical sensors OS1 to OS4. In the image forming apparatus, the imagesare written onto the photosensitive elements 11Y, 11M, 11C, and 11K bythe optical scanning as described above. The main-scanning direction inthe optical scanning is a direction perpendicular to the drawing of FIG.1 called “main-direction”. A method of measuring the toner density byusing the reflective optical sensors OS1 to OS4 is described below.

The optical scanning device 20 writes a certain electrostatic latentimage onto each of the photosensitive elements 11Y, 11M, 11C, and 11K;the developing devices GY, GM, GC, and GK develop the electrostaticlatent images to the toner images; the toner images are transferred fromthe photosensitive elements 11Y, 11M, 11C, and 11K directly to thesurface of the transfer belt 17. Thus, the toner pattern is formed. Itis clear from the above description that the transfer belt 17 works as“supporting member” in the first embodiment. This is why, the transferbelt 17 is called “supporting member 17”, appropriately. The tonerpattern is formed on the transfer belt 17, i.e., the supporting member,and is moved by the rotation of the transfer belt 17 to a detectionarea. After that, the toner-density measurement is performed by usingthe reflective optical sensors OS1 to OS4.

The toner pattern is removed from the surface of the transfer belt 17 bya cleaning device (not shown) arranged right, i.e., downstream of thereflective optical sensors OS1 to OS4.

FIG. 2 is a schematic diagram for explaining a relation between thetoner pattern that is formed on the transfer belt 17, i.e., thesupporting member and the reflective optical sensors OS1 to OS4.

The direction in which the reflective optical sensors OS1 to OS4 arearranged in FIG. 2 is the main-direction. On the other hand, thedirection, indicated by an arrow A, in which the transfer belt 17rotates is the sub-direction.

Position detecting patterns PP1 to PP4 are used to detect positions ofthe toner images in yellow to black, respectively. Toner patterns DP1 toDP4 are used to measure the toner density.

The toner pattern DP1 is used for the measurement of the yellow tonerdensity, the toner pattern DP2 is for the magenta toner density, thetoner pattern DP3 is for the cyan toner density, and the toner patternDP4 is for the black toner density.

In other words, the reflective optical sensors OS1 to OS4 detectpositions of the toner images at four points aligned in themain-scanning direction. Moreover, the reflective optical sensor OS1measures the yellow toner density, the reflective optical sensor OS2measures the magenta toner density, the reflective optical sensor OS3measures the cyan toner density, and the reflective optical sensor OS4measures the black toner density.

In the example illustrated in FIG. 2 the toner patterns DP1 to DP4 arealigned in the main-direction; however, it is possible to align thetoner patterns DP1 to DP4 in the sub-direction. In the later case, thereflective optical sensor OS1 sequentially measures the various tonerdensities. It is allowable to stop operation of the reflective opticalsensor OS4 and detect the position detecting patterns PP1 to PP3 at thethree points aligned in the main-scanning direction by using the otherthree reflective optical sensors OS1 to OS3.

As illustrated in FIG. 2, the position detecting patterns PP1 to PP4 areformed on certain positions of the transfer belt 17 to be opposed to thereflective optical sensors OS1 to OS4, respectively. Each of theposition detecting patterns PP1 to PP4 includes four pairs of linepatterns. Each pair includes a parallel line parallel to themain-direction and a slant line incline not parallel to themain-direction. The four pairs are formed with the yellow toner, themagenta toner, the cyan toner, and the black toner.

Although the reflective optical sensor detects the toner pattern that isformed on the transfer belt 17 that is used to convey the recordingsheet and transfer the toner image onto the recording sheet in the firstembodiment, the reflective optical sensor can be configured to detectthe toner pattern that is formed on the photosensitive element as thelatent-image carrier or the intermediate transfer belt (or intermediatetransfer medium).

The reflective optical sensors OS1 to OS4 and the measurement of thetoner pattern are described below. The four reflective optical sensorsOS1 to OS4 have the same structure, and therefore only the reflectiveoptical sensor OS1 is described. FIG. 3A is a schematic diagram of thereflective optical sensor OS1. The arrow in FIG. 3A corresponds to thesub-direction and a direction perpendicular to the sub-direction in theplane of the paper corresponds to the main-direction.

The reflective optical sensor OS1 includes a light-emitting unit and alight-receiving unit. The light-emitting unit and the light-receivingunit are accommodated in housing as a unit. The light-emitting unitincludes M-number of light-emitting elements E1 to E5 (M=5) that emits adetection light. The light-emitting elements E1 to E5 are alignedparallel to the main-direction at an equal pitch. The light-receivingunit includes N-number of light-receiving elements D1 to D5 (N=5) thatreceives a reflected light. The light-receiving elements D1 to D5 arealso aligned parallel to the main-scanning direction at an equal pitch,corresponding to the light-emitting elements E1 to E5. The reflectiveoptical sensor OS1 is arranged at the lower position on the transferbelt 17 as illustrated in FIG. 1.

The light-emitting elements E1 to E5 are aligned in the main-directionon positions corresponding to the light-receiving elements D1 to D5,respectively. As illustrated in FIG. 3B, when the light-emitting elementEi, where i is an arbitrary integer from 1 to 5, emits the detectionlight to the surface of the transfer belt 17 as the supporting member,the corresponding light-receiving element Di receives the detectionlight reflected from the transfer belt 17. It means that the pitchbetween adjacent ones of the light-receiving elements D1 to D5 is equalto the pitch between adjacent ones of the light-emitting elements E1 toE5.

To make the description simpler, the surface of the transfer belt 17 isassumed to be specular. When the light-emitting element emits thedetection light, the corresponding light-receiving element receives thedetection light specularly reflected from the surface of the transferbelt 17.

That is, the reflected light, illustrated in FIG. 3B that any of thelight-receiving elements D1 to D5 receives is a specular light reflectedfrom the surface of the transfer belt 17.

The light-emitting elements E1 to E5 are, for example, LEDs. Thelight-receiving elements D1 to D5 are, for example, PDs.

The pitch of the light-emitting elements E1 to E5 is set to such a valuethat, when the light-emitting elements E1 to E5 emit the detection lightand five spots of the detection light are formed on the surface of thetransfer belt 17 aligned in the main-scanning direction, a distancebetween adjacent ones of the spots is smaller than a width of the tonerpattern DP1 in the main-direction.

As described above, the toner pattern DP1 illustrated in FIG. 3A isformed with the yellow toner. The toner pattern DP1 includes variousrectangular toner patterns (five patterns in FIG. 2) having differentgradated densities. In other words, the toner pattern DP1 is acollection of the five rectangular having different toner densities.Those rectangular toner patterns having different toner densities areformed by adjusting a laser power in the optical scanning, a duty in theemission light, or a developing bias.

As illustrated in FIGS. 3A and 3B, the toner pattern DP1 is formed onthe surface of the transfer belt 17 as the supporting member, and thenis moved toward the detection area of the reflective optical sensor OS1.

Timing when the toner pattern DP1 is formed and time required for thetoner pattern DP1 to move to the detection area are substantially fixed.When the toner pattern DP1 approaches the detection area, thelight-emitting elements E1 to E5 start ON/OFF.

The detection of the position detecting pattern PP1 is performed beforethe detection of the toner pattern DP1. The detection of the positiondetecting pattern PP1 will be described later.

The size of the spot, which are formed on the surface of the transferbelt 17 when the light-emitting elements E1 to E5 emit the detectionlight, is set to, for example, 2 mm smaller than the pitch of thelight-emitting elements E1 to E5 of, for example, 3 mm. The five spotsare aligned in the main-direction on the transfer belt 17.

The width of each of the rectangular toner patterns of the toner patternDP1 in the main-direction is set to, for example, 2.5 mm smaller thanthe pitch of the light-emitting elements E1 to E5 of, for example, 3 mm.

That is, the distance between the adjacent spots in the main-directionis 1 mm, which is smaller than the width of the rectangular tonerpattern in the main-direction of 2.5 mm.

The light-emitting elements E1 to E5 turn ON/OFF, sequentially startingfrom the light-emitting element E1 to the light-emitting element E5.More particularly, the light-emitting element E1 turns ON and then OFF,firstly. The light-emitting element E2 turns ON and then OFF, secondly.After that, the light-emitting element E3 turns ON and then OFF,thirdly. Subsequently, the light-emitting element E4 and then thelight-emitting element E5 turn ON/OFF, in the same manner.

The ON/OFF operation of those light-emitting elements E1 to E5 isrepeated at a high speed. Thus, the surface of the transfer belt 17 isscanned in the main-direction over and over with the five spots of thedetection light. This operation is called, hereinafter, “spot scanningwith the detection light”.

As described above, the surface of the transfer belt 17 is specular. Ifthe detection light strikes an area out of the toner pattern, thereflected detection light is the specular light. The light-receivingelement Di, where i is an arbitrary integer from 1 to 5, is in positionto receive, when the detection light is specularly reflected from thearea out of the toner pattern, the specular light that has been emittedfrom the corresponding light-emitting element Ei only.

Consider, for example, a case where the center of the toner pattern DP1in the main-direction falls on the spot of the detection light that isemitted from the light-emitting element E3 under the above-describedconditions. As illustrated in FIG. 3C, when the light-emitting elementsE1, E2, E4, and E5 emit the detection light to the transfer belt 17, thedetection light is specularly reflected from the surface of the transferbelt 17, and then is received at the light-receiving elements D1, D2,D4, and D5, respectively.

On the other hand, when the light-emitting element E3 turns ON and emitsthe detection light to the toner pattern DP1, a part of the detectionlight is specularly reflected and the other part of the detection lightis diffusely reflected the toner pattern DP1.

An amount of the specular reflection component received at thelight-receiving element D3 decreases by an amount of the diffusionreflection component. The diffusion reflection light is received at theother light-receiving elements D1, D2, D4, and D5.

As a result, in the case where the light-emitting element E3 emits thedetection light, an output of the light-receiving element D3 isrelatively low (lower than the value when the detection light falls in aregion where there is no toner pattern), while outputs of the otherlight-receiving elements D1, D2, D4, and D5 are larger than zero.

It is possible to recognize from a result of the outputs that the tonerpattern DP1 (one of the rectangular toner patterns of the toner patternDP1) is on a position opposed to the light-emitting element E3 in themain-direction.

If the toner pattern is between the light-emitting elements E3 and E4,when the light-emitting element E3 turns ON, the output of thelight-receiving element D3 is low, and when the light-emitting elementE4 turns ON, the output of the light-receiving element D4 is low.

It is determined from a result of the outputs that the toner pattern isbetween the light-emitting elements E3 and E4 in the main-direction. Ifthe output of the light-receiving element D3 is lower than the output ofthe light-receiving element D4, the toner pattern is closer to thelight-emitting element E4.

In this manner, the position of the toner pattern DP1 in themain-direction can be detected accurately to one digit smaller than thepitch of the light-emitting elements E1 to E5 (e.g. down to aboutone-tenth of the pitch according to, for example, a ratio between theoutputs of the light-receiving elements D3 and D4).

It means that, if, for example, 100 light-emitting elements E1 to EM(M=100) are aligned at a 100-μm pitch in the main-direction, thearrangement width is 10 mm.

A total of 100 light-receiving elements D1 to DN (N=100) are aligned inthe main-direction at the 100-μm pitch in the same manner as thelight-emitting elements E1 to EM. When the light-emitting element Ei,where i is an arbitrary integer from 1 to 100, emits the detection lightto the supporting member, the detection light is specularly reflected,and is received at the corresponding light-receiving element Di. Thewidth of the toner pattern in the main-direction is equal to the pitchof the light-emitting elements E1 to EM of 100 μm. A change in theoutput of the light-receiving element Di is analyzed, while thelight-emitting elements E1 to E100 turn ON/OFF sequentially. If, when alight-emitting element Ej and a light-emitting element Ej+1 turn ON, theoutput of a light-receiving element Dj and the output of alight-receiving element Dj+1 are low, it is determined the that tonerpattern is between the light-emitting elements Ej and Ej+1 in themain-direction.

In other words, the position of the toner pattern having 100 μm in widthin the main-direction can be detected accurately by one digit smallerthan 100 μm.

It is easy to implement the arrangement of 100 light-emitting elementsat the 100-μm pitch, if an LED array is used. Moreover, it is easy toimplement the arrangement of 100 light-receiving elements at the 100-μmpitch, if a PD array is used. Even several tens- to several hundreds-μmpitch LED and PD arrays are available.

A reflective optical sensor including LEDs individually working as thelight-emitting elements E1 to E5 and PDs individually working as thelight-receiving elements D1 to D5 can be used as the reflective opticalsensor OS1 according to the first embodiment. The LEDs and the PDs areformed by resin molding or by surface mounting at an integrated andhigh-density manner. If extremely small LEDs and PDs dimensions of whichcan be adjusted in the millimeter are used, the pitch can be decreasedto about 1 mm.

By using extremely small LEDs and PDs the position of the toner patternwith 1 mm in the width in the main-direction can be detected accuratelydown to the millimeter.

As described above, the toner pattern DP1 is used to measure the yellowtoner density. The toner pattern DP1 includes the five rectangular tonerpatterns having different gradated densities aligned in thesub-direction at the predetermined pitch.

If, for example, the spot of the detection light emitted from thelight-emitting element E3 falls on the toner pattern while thelight-emitting elements E1 to E5 turn ON/OFF sequentially, the intensityof the specular reflection light received at the light-receiving elementD3 decrease while the outputs of the other light-receiving elementsincrease by the amount of the diffuse reflection light.

The amount of the specular reflection light is inversely proportional tothe toner density, while the amount of the diffusion reflection light isdirectly proportional to the toner density.

Therefore, the toner density of the toner pattern can be measured fromthe output of the light-receiving element D3 representing the specularreflection light and the outputs of the other light-receiving elements.More particularly, those outputs are amplified by an amplifier (notshown), and then subjected to a desired signal processing. After that,the toner density is calculated from the processed signal by using atoner-density calculating process.

An algorism for calculating the toner density is determinedexperimentally based on a practical embodiment of the image formingapparatus.

In this manner, the toner density is measured accurately by emitting thedetection light from the reflective optical sensor to the correctposition of the toner pattern.

Moreover, because the light-emitting elements and the light-receivingelements that are aligned at a very small pitch, even if the width ofthe toner pattern in the main-direction is small, the position of thetoner pattern in the main-direction is detected accurately in such smallunit the same as the pitch.

In the first embodiment, if independent extremely small LEDs and PDsaligned at about 1-mm pitch are used as the light-emitting elements E1to E5 and the light-receiving elements D1 to D5, the width of the tonerpattern DP1 in the main-direction is enough to about 1 mm. If the tonerpattern DP1 includes the five rectangular toner patterns as illustratedin FIG. 3A, the width of each toner pattern in the sub-direction isenough to smaller than about 1 mm.

Then, the area of the toner pattern DP1 is 5 mm², which is equal to1/125 of the conventional toner pattern of 25 mm×25 mm. Because the areaof the toner pattern DP1 is small, the toner pattern DP1 can be formedwithin a short time. This makes it possible to suppress a reduction inthe operating efficiency of the image formation. Moreover, the amount ofthe toner for the toner pattern is remarkably decreased to 1/125 in thesame ratio as the area of the toner pattern is decreased.

The reflective optical sensor can detect the relative position of thetoner images in the sub-direction and the positions of the toner imagesin the main-direction by using the position detecting pattern PP1 or thelike.

FIGS. 3D to 3F are schematic diagrams for explaining the positiondetection by using the position detecting pattern PP1.

The position detecting pattern PP1 includes parallel line patterns LPY1,LPM1, LPC1, and LPK1 each parallel to the main-direction, and slant linepatterns LPY2, LPM2, LPC2, and LPK2 each not parallel to themain-direction.

The line patterns LPY1 and LPY2 make a pair, and are formed with theyellow toner.

The line patterns LPM1 and LPM2 make a pair, and are formed with themagenta toner. The line patterns LPC1 and LPC2 make a pair, and areformed with the cyan toner. The line patterns LPK1 and LPK2 make a pair,and are formed with the black toner.

The four pairs of the line patterns are formed in such a manner that thepairs are to be aligned in the sub-direction at a fixed interval.

If the pairs are actually aligned at the fixed interval in thesub-direction, it is determined that the positional relation among theyellow toner image, the magenta toner image, the cyan toner image, andthe black toner is correct in the sub-direction.

To determine whether the positional relation in the sub-direction iscorrect, for example as illustrated in FIG. 3D, the light-emittingelement E3 turns ON when the position detecting pattern PP1 comes closeto the detection area of the reflective optical sensor. Thelight-emitting element E3 is ON for a continuous time.

As the position detecting pattern PP1 moves, the spot of the detectionlight emitted from the light-emitting element E3 relatively moves in thesub-direction on the supporting member, thereby illuminating the linepatterns LPY1 to LPK1 one by one.

When the detection light falls on any of the line patterns, the outputof the light-receiving element D3, which receives the specularreflection light, decreases while the outputs of the otherlight-receiving elements, which receives the diffuse reflection light,increases. Therefore, time that the detection light takes to movethrough the intervals among the four line patterns can be measured bytracking the outputs of the light-receiving elements D1 to D5 in termsof time.

If the time intervals are equal, it is determined that the positionalrelation among the toner images in the sub-direction is correct. If thetime intervals are not equal, it is determined that the positionalrelation is not correct. Moreover, a deviation amount in the positionalrelation can be measured from the change in the outputs. If thepositional relation is not correct, the timing to start the opticalscanning is adjusted based on the deviation amount.

On the other hand, the positional relation in the main-direction amongthe toner images is determined in the following manner. In the followingdescription, the position of the yellow toner image is detected withreference to FIGS. 3E and 3F as an example.

FIG. 3E is a schematic diagram of the yellow toner image that isarranged in a correct position. It takes time T for the spot of thedetection light to move from the line pattern LPY1 to the line patternLPY2.

FIG. 3F is a schematic diagram of the yellow toner image that isarranged in an incorrect position deviated by ΔS in the main-direction.Because the line pattern LPY2 is not parallel to the line pattern LPY1,time required for the spot of the detection light to move from the linepattern LPY1 to the line pattern LPY2 is longer, i.e., T+ΔT. Therefore,the deviation amount is calculated from ΔT that is a difference betweenT and T+ΔT.

More particularly, the relation between ΔS and ΔT is as follows:ΔS·tan θ=V·ΔTwhere θ is angle between the line pattern LPY2 and the main-direction,and V is velocity of the transfer belt 17 as the supporting member inthe sub-direction. Therefore, ΔS is calculated as follows:ΔS=V·ΔT·cot θ

As described with reference to FIGS. 3A to 3C, in the reflective opticalsensor OS1, the light-emitting elements E1 to E5 turn ON/OFFsequentially to detect the toner patterns. It takes a certain time fromthe ON/OFF of the light-emitting element E1 to the ON/OFF of thelight-emitting element E5. The certain time is called “scanning time”.

The toner pattern (i.e., individual rectangular toner patterns) shouldbe within an area to be subjected to the spot scanning by the reflectiveoptical sensor (i.e., area where the sequentially flashing spots of thedetection light falls) (hereinafter, “scanning area”) during thescanning time. In other words, the sequential ON/OFF of thelight-emitting elements E1 to E5 are performed while the toner patternis within the scanning area.

If M, which is the number of the light-emitting elements of thereflective optical sensor, is small, the scanning time will be short.

As described above, to maintain the operating efficiency of the imageformation by decreasing the time to form the toner pattern andefficiently reduce the amount of the toner for the toner pattern, it isnecessary that the toner pattern be small.

To correctly exposing the small toner pattern to the detection light,thereby measuring the correct toner density, it is necessary to decreasethe pitch of the light-emitting elements and the light-receivingelements by an amount that corresponds to the decrease in the width ofthe toner pattern in the main-direction.

The length of the arrangement area of the light-emitting elements andthe light-receiving elements is required to be about 10 mm inconsideration for the miss-match between the toner pattern and thereflective optical sensor in the main-direction. As the pitch decreases,M, which is the number of the light-emitting elements, increases to aremarkably large number.

As M increases, the scanning time increases.

The supporting member with the toner pattern formed thereon moves by adistance V·st in the sub-direction for the scanning time, where st isscanning time and V is velocity of the supporting member moving in thesub-direction.

If M is too large while V is unchanged, the scanning time becomes longerthan time required for the toner pattern to pass through the scanningarea. If so, it is difficult to measure the correct toner density.

A second embodiment and a third embodiment of the present inventiondisclose a solution to this problem and those embodiments are describedwith reference to FIGS. 4A and 4B, respectively. Reflective opticalsensors according to the second embodiment and the third embodimentinclude 15 light-emitting elements E1 to E15 and 15 light-receivingelements D1 to D15. The light-emitting elements E1 to E15 correspondsthe light-receiving elements D1 to D15, respectively in the one-to-onemanner. Although the light-emitting elements and the light-receivingelements illustrated in FIGS. 4A and 4B are 15, each, several tens toseveral hundreds of the light-emitting elements and the light-receivingelements are used in practice. To make the drawings simpler, the numberof the light-emitting elements and the light-receiving elements is setto 15 in the second embodiment and the third embodiment. In other words,the light-emitting elements and the light-receiving elements can be morethan 15 or less than 15.

In the second embodiment illustrated in FIG. 4A, the light-emittingelements E1 to E15 and the light-receiving elements D1 to D15 that arealigned in the main-direction sequentially with beginning with thelight-emitting element E1 and the light-receiving element D1. Moreover,the light-emitting elements E1 to E15 and the light-receiving elementsD1 to D15 that are divided into a first group, a second group, and athird group. The first group includes the light-emitting elements E1 toE5 and the light-receiving elements D1 to D5; the second group includesthe light-emitting elements E6 to E10 and the light-receiving elementsD6 to D10; and the third group includes the light-emitting elements E11to E15 and the light-receiving elements D11 to D15. The light-emittingelements of each group are aligned in a single line, and thelight-receiving elements of each group are aligned in a single line.When the reflective optical sensor is in position to measure the tonerdensity, the line of the second group is shifted by ΔL from the line ofthe first group in the sub-direction, and the line of the third group isshifted by ΔL from the line of the second. The distance ΔL is decidedbased on the velocity of the supporting member moving in thesub-direction.

The light-emitting elements E1 to E15 turn ON/OFF sequentially while thetoner pattern is moving in the sub-direction at the velocity of V.

Time required for ON/OFF of the light-emitting elements E1 to E5, timerequired for ON/OFF of the light-emitting elements E6 to E10, and timerequired for ON/OFF of the light-emitting elements E11 to E15 are equal,more particularly, st/3, where st is scanning time.

The toner pattern moves by distance V·st/3 in the sub-direction in timest/3. Therefore, if ΔL is set as follows:ΔL=V·st/3then the spot scanning of the toner pattern by the light-emittingelements E1 to E15 is completed within the scanning time.

In the third embodiment illustrated in FIG. 4B, when the reflectiveoptical sensor is in position to measure the toner density, thelight-emitting elements E1 to E15 and the light-receiving elements D1 toD15 are aligned in a single direction that is inclined to themain-direction at an angle α. The angle α is decided based on thevelocity of the supporting member moving in the sub-direction.

More particularly, if the angle α satisfies a following Equation:Z·tan α=V·stwhere st is scanning time, Z is the length in the main-direction oflines on which the light-emitting elements E1 to E15 and thelight-receiving elements D1 to D15 are aligned, then the spot scanningof the toner pattern by the light-emitting elements E1 to E15 iscompleted within the scanning time.

In a fourth embodiment of the present invention as illustrated in FIG.5, the spot scanning is optimized as follows.

A reflective optical sensor according to the fourth embodiment includes15 light-emitting elements and 15 light-receiving elements. Thelight-emitting elements correspond to the light-receiving elements,respectively in the one-to-one manner. Although the light-emittingelements and the light-receiving elements illustrated in FIG. 5 are 15,each, several tens to several hundreds of the light-emitting elementsand the light-receiving elements are used in practice. To make thedrawings simpler, the number of the light-emitting elements and thelight-receiving elements is set to 15 in the fourth embodiment. In otherwords, the light-emitting elements and the light-receiving elements canbe more than 15 or less than 15.

When the reflective optical sensor is in position to measure the tonerdensity, the direction in which the 15 light-emitting elements arealigned and the direction in which the 15 light-receiving elements arealigned are substantially parallel to the main-direction.

Each of the 15 light-emitting elements makes a pair with a correspondingone of the 15 light-receiving elements. The light-emitting elements andthe light-receiving elements are divided into three groups G1, G2, andG3. The groups G1, G2, and G3 are aligned in a single line extending inthe main-direction.

The group G1 includes five pairs, more particularly, the light-emittingelements E11 to E15 and the light-receiving elements D11 to D15. Thegroup G2 includes five pairs, more particularly, the light-emittingelements E21 to E25 and the light-receiving elements D21 to D25. Thegroup G3 includes five pairs, more particularly, the light-emittingelements E31 to E35 and the light-receiving elements D31 to D35.

All the three groups G1, G2, and G3 have the same structure.

When the reflective optical sensor is in position to measure the tonerdensity, the first light-emitting element of each group, i.e., thelight-emitting elements E11, E21, and E31 turn ON/OFF simultaneously.Then, the second light-emitting element of each group, i.e., thelight-emitting elements E12, E22, and E32 turn ON/OFF simultaneously.After that, the light-emitting elements E13, E23, and E33, thelight-emitting elements E14, E24, and E34, and the light-emittingelements E15, E25, and E35 turn ON/OFF sequentially.

With this configuration, the scanning time can be decreased to one-thirdof the scanning time in the second embodiment and the third embodiment.Therefore, the spot scanning is completed while the toner pattern ispassing through the scanning area.

As a variation of the fourth embodiment, it is allowable to shift thelight-emitting elements and the light-receiving elements other than thelight-emitting elements E11, E21, and E31 and the light-receivingelements D11, D21, and D31 in the sub-direction with the light-emittingelements E11, E21, E31 and the light-receiving elements D11, D21, D31maintained at their respective positions illustrated in FIG. 5 in such amanner that the light-emitting elements and the light-receiving elementsare aligned in a direction that is inclined to the main-direction at acertain angle. The certain angle is decided based on the velocity of thesupporting member moving in the sub-direction, in the same manner as inthe third embodiment.

More light-emitting elements and light-receiving elements are used inthe second, the third, and the fourth embodiments as compared to thefirst embodiment. If the pitch is unchanged, the length of thereflective optical sensor in the main-direction, i.e., the sensing areaincreases. In other words, an allowable extent of the positionalmiss-match in the main-direction between the toner pattern and thereflective optical sensor increases. On the other hand, if the length ofthe reflective optical sensor is unchanged, the pitch between adjacentlight-emitting elements and light-receiving elements decreases. Thisresults in an increase in the spatial resolution in the main-direction.

As described above, M, which is the number of the light-emittingelements, can be set unequal to N, which is the number of thelight-receiving elements. In fifth to seventh embodiments of the presentinvention illustrated in FIGS. 6A to 6C, respectively, M is not equal toN.

In the fifth embodiment illustrated in FIG. 6A, N is 15 and M is 30.

The light-emitting unit includes 15 light-emitting elements E11, . . . ,E1 i . . . , and E115 that are aligned in a single line extending in themain-direction at an equal pitch, and 15 light-emitting elements E21, .. . , E2 i . . . , and E215 that are aligned in another single lineextending in the main-direction at an equal pitch. Positions of thelight-emitting elements E21, . . . , E2 i . . . , and E215 in themain-direction are the same as positions of the light-emitting elementsE11, . . . , E1 i . . . , and E115, respectively.

The light-receiving unit includes 15 light-receiving elements D1, . . ., Di . . . , and D15 that are aligned in a line extending in themain-direction at an equal pitch between the two lines of thelight-emitting elements. Positions of the light-receiving elements D1, .. . , Di . . . , and D15 are the same in the main-direction as thepositions of the light-emitting elements E11, . . . , E1 i . . . , andE115, respectively, i.e., the same in the main-direction as thepositions of the light-emitting elements E21, . . . E2 i . . . , andE215, respectively.

The light-emitting elements E11 and E21, which are aligned in the sameposition in the main-direction, turn ON/OFF simultaneously. After that,the light-emitting elements E12 and E22 turn ON/OFF, simultaneously. TheON/OFF operation is repeated in the same manner until the light-emittingelements E115 and E215 turn ON/OFF. Thus, the output of the detectionlight that illuminates the supporting member and the toner patternbecomes about double.

The output of the LEDs, which are used as the light-emitting elements,in general, depends on not the light-emitting-element area but theapplied current density.

If the applied current density increases, the output increases but thelifetime of the LEDs decreases. To maintain the lifetime, the appliedcurrent density be preferably lower than a certain level. If thelight-emitting-element area increases (with the applied current densityunchanged), the applied current amount increases. However, an increasein the light-emitting-element area results in an increase of spots forilluminating the supporting member and the toner pattern.

To solve this problem, it is preferable to double the output of thelight. This has been achieved by arranging the two lines oflight-emitting units, as illustrated in FIG. 6A, with both thelight-emitting-element area and the current density unchanged.

In the sixth embodiment illustrated in FIG. 6B, N is 30 and M is 15.

The light-receiving unit includes 15 light-receiving elements D11, . . ., D1 i . . . , and D115 that are aligned in a single line extending inthe main-direction at an equal pitch, and 15 light-receiving elementsD21, . . . D2 i . . . , and D215 that are aligned in another single lineextending in the main-direction at an equal pitch. The light-emittingunit includes 15 light-emitting elements E1, . . . , Ei . . . , and E15that are aligned in a single line extending in the main-direction at anequal pitch between the two lines of the light-receiving elements.Positions of the light-emitting element Ei, the light-receiving elementD1 i, and the light-receiving element D2 i, where i is an arbitraryinteger from 1 to 15, are the same in the main-direction.

Because PDs, which receive the detection light (reflected light), arealigned in the two lines, the light-receiving sensitivity becomesdouble. Alternatively, if the light-receiving-element area in thesub-direction is increased to double with the PDs being aligned in asingle line, the light-receiving sensitivity increases. However, theincrease in the light-receiving sensitivity is relatively small,especially when the size of the spot of the detection light reflectedfrom the supporting member and the toner pattern is small. From theviewpoint of the improvement of the light-receiving sensitivity, it ismore effective to arrange the PDs in the two lines symmetrically in thesub-direction and the LEDs between the two lines, as illustrated in FIG.6B.

In the first to the sixth embodiments as described with reference toFIGS. 2 to 6B, the light-emitting elements and the light-receivingelements are aligned at the equal pitches, and the pitch of thelight-emitting elements is equal to the pitch of the light-receivingelements. However, it is possible to set the pitch of the light-emittingelements different from the pitch of the light-receiving elements.

A seventh embodiment according to the present invention in which thepitch of the light-emitting elements different from the pitch of thelight-receiving elements is described with reference to FIG. 6C. In theseventh embodiment, there are seven light-emitting elements E1, . . . ,Ei, . . . , and E7 and 14 light-receiving elements D1, . . . , Di, . . ., and D14. The light-receiving elements are aligned at a pitch half ofthe pitch of the light-emitting elements. Each of the light-emittingelements E1 to E7 corresponds to two light-receiving elements. In thismanner, the spatial resolution in the main-direction in increased bydecreasing the pitch of the PDs.

If the reflective optical sensor is arranged in a line not parallel tothe main-scanning direction, the higher spatial resolution in themain-direction is obtained.

Assume, more particularly, that the reflective optical sensor isarranged in such a manner that an angle between the main-scanningdirection and the lines on which the light-emitting elements and thelight-receiving elements are aligned is β, and the pitch of thelight-emitting elements and the light-receiving elements is pt. Then,the pitch of points in the main-direction projected from thelight-emitting elements and the light-receiving elements is decreased topt·cos β, i.e., the spatial resolution increases.

In the above-described embodiments, the LEDs and the PDs are formed asthe light-emitting elements and the light-receiving elements by theresin molding or by the surface mounting at an integrated andhigh-density manner. As described above, if extremely small LEDs and PDsdimensions of which can be adjusted in the millimeter are used, thepitch can be decreased to about 1 mm.

To increase the spatial resolution, it is necessary basically todecrease the pitch of the light-emitting elements and thelight-receiving elements. In an LED array and a PD array in which LEDsand PDs are integrally arranged, the pitch is extremely small. The LEDarray and the PD array are used in an eighth embodiment and a ninthembodiment of the present invention.

In the eighth embodiment illustrate in FIG. 7A, a reflective opticalsensor OS11 includes an LED array (light-emitting unit) EA and a PDarray (light-receiving unit) DA. The LED array EA includes six LEDs asthe light-emitting elements E1 to E6 integrally aligned in a single lineat an equal pitch on the same substrate. The PD array DA includes sixPDs as the light-receiving elements D1 to D6 integrally aligned in asingle line at an equal pitch on the same substrate. The LED array EAand the PD array DA are accommodated in the same housing of thereflective optical sensor OS11.

In the ninth embodiment illustrate in FIG. 7B, a reflective opticalsensor OS12 includes a light-emitting/receiving unit array DEA. Thelight-emitting/receiving unit array DEA includes six LEDs as thelight-emitting units E1 to E6 and six PDs as the light-receivingelements D1 to D6 arranged on the same substrate. The six LEDs arealigned in a single line at an equal pitch. The six PDs are aligned in asingle line at an equal pitch. The light-emitting/receiving unit arrayDEA is accommodated in the same housing of the reflective optical sensorOS12.

As illustrated in FIGS. 7A and 7B, the pitch of the light-emittingelements is equal to the pitch of the light-receiving elements. Aposition of each light-emitting element in the main-direction is thesame as a position of the corresponding light-receiving element.However, in the same manners as in the fifth to the seventh embodimentsillustrated in the FIGS. 6A to 6C, the number of and the pitch of thelight-emitting elements can be different from the number of and thepitch of the light-receiving elements.

To make the drawings and the description simpler, only sixlight-emitting elements and six light-receiving elements are illustratedin FIGS. 7A and 7B. In other words, the light-emitting elements and thelight-receiving elements can be more than six or less than six.

In this manner, if the LED array and the PD array are used as thelight-emitting unit and the light-receiving unit, the pitch of thelight-emitting elements and the light-receiving elements can be fromseveral tens of micrometers to several hundreds of micrometers. In otherwords, an extremely high spatial resolution can be obtained.

If the LED array and the PD array that are fabricated by thesemiconductor processing are used instead of individual LEDs and PDs, itis possible to obtain a remarkably high positional accuracy in thelight-emitting elements and the light-receiving elements.

In the ninth embodiment illustrated in FIG. 7B, because the LED arrayand the PD array are integrally formed on the same substrate, a relativepositioning between the light-emitting elements and the light-receivingelements can be done extremely accurately.

As for the reflection properties of the toner patterns, the tonerpattern in each color has different dependency to the wavelength.However, the toner pattern in each color has almost the same dependencyto the near-infrared or infrared rays, especially, to rays having awavelength within a rage from 800 nm to 1000 nm.

Therefore, the light-emitting elements in the reflective optical sensorpreferably emit a light having a wavelength within the above range.Moreover, the LEDs forming the light-emitting unit preferably emit thelights having the same wavelength.

From the viewpoint of the wavelength, usage of the LED array as thelight-emitting unit is preferable because the LEDs emit the lightshaving the same wavelength on the processing basis.

If the wavelength sensitivities of N-number of the light-receivingelements forming the light-receiving unit are different from each other,even if the light-receiving elements receive the same light reflectedfrom the toner pattern, the outputs of the light-receiving elementsdiffers from each other, which may cause an error in the calculation forthe toner density.

Therefore, it is preferable to use PDs having the same peak sensitivitywavelength as the light-receiving elements of the light-receiving unit.From the viewpoint of the peak sensitivity wavelength, usage of the PDarray as the light-receiving unit is preferable because the PDs of thePD array have the same peak sensitivity wavelength on the processingbasis.

From the viewpoint of efficiency in receiving the detection lightemitted from the light-emitting unit by the light-receiving unit, it ispreferable to substantially match the wavelength of the detection lightemitted from the LEDs forming as the light-emitting unit with the peaksensitivity wavelength of the PDs forming the light-receiving unit in anaccurate manner by several tens of nanometers. A wavelength of a lightemitted from a typical GaAs-based LED is about 950 nm. A peaksensitivity wavelength of a typical Si-based PD is from 800 nm to 1000nm. Therefore, the typical GaAs-based LEDs and the typical Si-based PDsare preferable as the light-emitting elements and the light-receivingelements.

It is possible to shift the wavelength band by adjusting thecompositions or the structure of the LEDs and the PDs. Thus, thewavelength of the detection light emitted from the LEDs can be setsubstantially matched with the peak sensitivity wavelength of the PDs.

As described above, in the reflective optical sensor, the light-emittingelements of the light-emitting unit emit the spots of the detectionlight onto the supporting member or the toner pattern.

If individual LEDs each integrally including a member having the lensfunction of collecting divergent light are used as the light-emittingelements, the LEDs form the spots of the detection light all alone.

If an LED array that does not has the lens function of collecting thedetection light is used as the light-emitting unit, it is necessary toadd an illumination optical system that receives the detection lightfrom the light-emitting elements and collects and guides the detectionlight to the surface of the supporting member and/or a light-receivingoptical system that receives the light reflected from the surface of thesupporting member and collects and guides the reflected light to thelight-receiving elements. By the usage of the illumination opticalsystem and/or the light-receiving optical system, the spots of thedetection light can be formed.

Even if individual LEDs having the lens function of collecting thedetection light are used as the light-emitting elements, it is allowableto add the illumination optical system and/or the light-receivingoptical system to form the spots of the detection light in a moreefficient manner.

A tenth embodiment of the present invention is described with referenceto FIGS. 8A to 8C.

FIG. 8A is a schematic diagram of a reflective optical sensor OSaccording to the tenth embodiment, viewed in the main-direction.

The light-emitting unit includes five individual LEDs, as thelight-emitting elements E1 to E5, aligned in a single line extending inthe main-direction at an equal pitch. The light-receiving unit includesfive individual PDs, as the light-receiving elements D1 to D5, alignedin a single line extending in the main-direction at an equal pitch. TheLEDs as the light-emitting elements has the lens function of collectingthe divergent light.

The reflective optical sensor OS includes an illumination optical systemLE and a light-receiving optical system LD. The illumination opticalsystem LE and the light-receiving optical system LD can be, asillustrated in FIGS. 8A to 8C, cylindrical lenses. The cylindricallenses have a positive power in the sub-direction. The supporting member17 is, more particularly, the transfer belt. A toner pattern DP is usedfor the toner-density measurement.

The process of measuring the toner density is performed in the samemanner as described above with reference to FIGS. 2 and 3.

When the light-emitting element (LED) Ei, where i is an arbitraryinteger from 1 to 5, turns ON/OFF, the detection light is collected inthe sub-direction by the illumination optical system LE, and thecollected detection light illuminates the supporting member 17 or thetoner pattern DP. The reflected light is collected in the sub-directionby the light-receiving optical system LD, and the collected reflectedlight is received by the light-receiving element Di.

The illumination optical system can be used to shape the detection lightso that the spot having a desired shape is formed on the supportingmember or the toner pattern. The light-receiving optical system can beused to shape the reflected light so that the spot having a desiredshape is formed on the light-receiving elements.

If the illumination optical system and the light-receiving opticalsystem have the same structure, the costs for those optical systems canbe suppressed. To make the drawings and the description simpler, onlyfive light-emitting elements and five light-receiving elements areillustrated in FIGS. 8A to 8C. In other words, the light-emittingelements and the light-receiving elements can be more than five or lessthan five.

A reflective optical element OSA according to an eleventh embodiment ofthe present invention is described with reference to FIGS. 9A and 9B.The reflective optical element OSA includes the illumination opticalsystem and the light-receiving optical system. As illustrated in FIG.9A, the illumination optical system includes light-collecting lenses LE1to LE5 in positions to receive the detection light from five LEDs as thelight-emitting elements E1 to E5, respectively. The light-collectinglenses LEi, where i is an arbitrary integer from 1 to 5, receives thedetection light as divergent light from the corresponding light-emittingelement Ei, and collects the detection light. Thus, the efficiency inillumination to the supporting member 17 increases. As compared to thecylindrical lens that is used as the illumination optical systemillustrated in FIGS. 8A to 8C, if lenses having the collecting power inthe main-direction are used, the efficiency in the illuminationincreases more.

Anamorphic lenses having a power in the main-direction different from apower in the sub-direction can be used as the light-collecting lens LEi,where i is an arbitrary integer from 1 to 5.

It is allowable to use the illumination optical system, which isillustrated in FIG. 9A, formed with the anamorphic lens LEicorresponding to the light-emitting element Ei in the one-to-one manner,and the light-receiving optical system, which is illustrated in FIG. 8C,formed with the cylindrical lenses having only a power in thesub-direction. A user can select a combination of a type of theillumination optical system and a type of the light-receiving opticalsystem as appropriately, taking into consideration desired illuminationefficiency, a shape of the spots of the detection light, desiredlight-receiving efficiency, and a shape of the spots on thelight-receiving elements. To make the drawings and the descriptionsimpler, only five light-emitting elements and five light-receivingelements are illustrated in FIGS. 9A and 9B. In other words, thelight-emitting elements and the light-receiving elements can be morethan five or less than five.

A twelfth embodiment and a thirteenth embodiment of the presentinvention are described with reference to FIGS. 10A and 10B.

In the twelfth embodiment illustrated in FIG. 10A, a reflective opticalsensor OSB includes the light-emitting unit and an illumination opticalsystem LEA. The light-emitting unit includes six LEDs as thelight-emitting elements E1 to E6. The illumination optical system LEAincludes convex lenses integrally arranged on a surface. The convexlenses are in positions to receive the detection light from thelight-emitting elements E1 to E6, respectively and collect the receiveddetection light.

As illustrated in FIG. 10A, although the surface facing the LEDs cancollect the light, the opposite surface is flat, i.e., cannot collectthe light. However, it is allowable to use surfaces that can collect thelight on the both sides. Because the illumination optical system LEA isintegrally formed, as compared to attaching individual lensescorresponding to the light-emitting elements, the illumination opticalsystem LEA is easy to attach and has an advantage in the arrangementaccuracy among the lens surfaces.

Although not illustrated in FIG. 10A, it is possible to use a collectionof integrally-formed light-receiving lenses as the light-receivingoptical system in the same manner as the light-emitting optical system.

In the thirteenth embodiment illustrated in FIG. 10B, anillumination/light-receiving optical system LEDA includes sixlight-collecting lenses LE1 to LE6 as the illumination optical systemand six light-collecting lenses LD1 to LD6 as the light-receivingoptical system as a unit. Relative positions among those components arefixed, as appropriately.

Usage of the illumination/light-receiving optical system LEDA makes itpossible to increase the accuracy in arrangement of the light-collectinglenses for the illumination optical system and the light-collectinglenses for the light-receiving optical system. Those light-collectinglenses can be formed on a substrate made of, for example, glass or resinat the positions as illustrated in FIG. 10B by the photolithography orthe nanoimprint technology.

To make the drawings and the description simpler, six light-emittingelements and six light-receiving are elements illustrated in FIGS. 10Aand 10B. In other words, the light-emitting elements and thelight-receiving elements can be more than six or less than six.

If, for example, the light-emitting elements and the light-receivingelements are aligned as illustrated in FIG. 4A, 4B, 6A, 6B, or 6C, thearrangements of the illumination optical system and the light-receivingoptical system are changed as appropriately based on the arrangements ofthe light-emitting elements and the light-receiving elements.

If the illumination optical system and the light-receiving opticalsystem are lens arrays or lens-surface arrays, the pitch of the lensesor the lens surfaces is preferably set equal.

A toner-density measuring method according to a fourteenth embodiment ofthe present invention is described below.

In the reflective optical sensor that has been described with referenceto FIGS. 3A to 3C, the light-emitting elements correspond to thelight-receiving elements in the one-to-one manner. When any one of thelight-emitting elements emits the detection light to the area out of thetoner pattern of the supporting member, only the correspondinglight-receiving element receives the detection light reflected from thesupporting member as the specular light.

In a first example, when the light-emitting element E3 emits thedetection light to the area out of the toner pattern, only thelight-receiving light D3 receives the detection light and the otherlight-receiving elements receive no light.

On the other hand, when the light-emitting element E3 emits thedetection light to the toner pattern, the detection light is diffuselyreflected by the toner pattern. As a result, not only thelight-receiving element D3 but also the other light-receiving elementsD1, D2, D4, and D5 receive the detection light.

The outputs in the first example are illustrated in FIGS. 11A and 11B.

FIG. 11A is a bar chart of the outputs of the light-receiving elementsD1 to D5 when the light-emitting element E3 emits the detection light tothe surface of the supporting member, i.e., an area out of the tonerpattern. In this case, because the detection light is specularlyreflected by the area out of the toner pattern, only the light-receivingelement D3 receives the detection light, and the other light-receivingelements D1, D2, D4, and D5 receive no light.

FIG. 11B is a bar chart of the outputs of the light-receiving elementsD1 to D5 when the light-emitting element E3 emits the detection light tothe toner pattern. In this case, because the detection light isdiffusely reflected by the toner pattern, not only the light-receivingelement D3 but also the other light-receiving elements D1, D2, D4, andD5 receive the detection light.

The amount of the specular reflection light is in inverse proportion tothe toner density; and the amount of the diffusion reflection light isin proportion to the toner density. Therefore, the toner density of thetoner pattern can be calculated from the output of the light-receivingelement D3, which representing the amount of the specular reflectionlight, and the outputs of the other light-receiving elements D1, D2, D4,and D5 by using a predetermined algorism.

In the first example, output representing the specular reflection light(hereinafter, “specular reflection output”) is clearly differentiatedfrom output representing the diffuse reflection light (hereinafter,“diffuse reflection output”). More particularly, when the light-emittingelement Di emits the detection light, the output of the correspondinglight-receiving element Di is the specular reflection output, and theoutputs of the non-corresponding light-receiving elements Dj, where j≠i,are the diffuse reflection output. Therefore, the algorism that is usedin the toner-density calculation is simple.

However, in some embodiments of the reflective optical sensors, it isdifficult to clearly differentiate the specular reflection output fromthe diffuse reflection output. Some outputs may be mixtures of thespecular reflection output and the diffuse reflection output.

Even in the reflective optical sensor illustrated in FIGS. 3A to 3Cincluding the five light-emitting elements E1 to E5 and the fivelight-receiving elements D1 to D5, if the pitch of the light-receivingelements D1 to D5 is decreased to a small value as the pitch of thelight-emitting elements E1 to E5 decreases and/or if the diameter of thedetection light is larger than the pitch of the light-receiving elementsD1 to D5 because the detection light emitted from the light-emittingelement Ei is the divergent light and the detection light, even afterspecularly reflected from the surface of the supporting member, goestoward the light-receiving elements in the divergence manner, thespecular reflection output may disadvantageously be mixed with thediffuse reflection output.

A second example is described with the reflective optical sensor OS1illustrated in FIGS. 3A to 3C.

As described above, the surface of the transfer belt 17 is specular. Thedetection light that is reflected from the area out of the toner patternis the specular reflection light.

The light-emitting elements E1 to E5 emit the detection light,sequentially. When the light-emitting element Ei, where i is anarbitrary integer from 1 to 5, emits the detection light to the area outof the toner pattern, the corresponding light-receiving element Di andthe adjacent light-receiving elements Dj, where j=i±1, receive thereflected detection light as the specular light.

FIG. 12A is a bar chart of the outputs of the light-receiving elementsD1 to D5 when the light-emitting element E3 emits the detection light tothe area out of the toner pattern.

The light-receiving elements D2, D3, and D4 receive the specularreflection light from the transfer belt 17, while the outputs of thelight-receiving elements D1 and D5 are zero.

Consider a case where the center of the toner pattern DP1 in themain-direction is at a position to be exposed with the spot of thedetection light emitted from the light-emitting element E3, on theconditions that if the light-emitting element Ei emits the detectionlight to the area out of the toner pattern, the correspondinglight-receiving element Di and the adjacent light-receiving elements Dj(where j=i±1) receives the reflected detection light as the specularlight.

In this case, when the light-emitting element E1 emits the detectionlight, the detection light is specularly reflected from the surface ofthe transfer belt 17, and then received at the light-receiving elementsD1 and D2. When the light-emitting element E2 emits the detection light,the detection light is specularly reflected from the surface of thetransfer belt 17, and then received at the light-receiving elements D1,D2, and D3.

When the light-emitting element E4 emits the detection light, thedetection light is specularly reflected from the surface of the transferbelt 17, and then received at the light-receiving elements D3, D4, andD5. When the light-emitting element E5 emits the detection light, thedetection light is specularly reflected from the surface of the transferbelt 17, and then received at the light-receiving elements D4 and D5.

When the light-emitting element E3 emits the detection light, thedetection light is specularly and diffusely reflected from the tonerpattern DP1.

The amount of the specular reflection component received at each of thelight-receiving elements D2, D3, and D4 decreases due to the diffusereflection. On the other hand, the diffuse reflection light is receivedat not only the light-receiving element D3 but also the light-receivingelements D1, D2, D4, and D5.

FIG. 12B is a bar chart of the outputs of the light-receiving elementsD1 to D5 when the light-emitting element E3 emits the detection light tothe toner pattern DP1.

It is clear from comparison of FIG. 12A with FIG. 12B, the output of thelight-receiving element D3, which is corresponding to the light-emittingelement E3, represents only the specular light reflected from thesupporting member or the toner pattern.

The outputs of the light-receiving elements D1 and D5, which arenon-corresponding to the light-emitting element E3, represent only thediffuse light reflected from the toner pattern.

The outputs of the light-receiving elements D2 and D4, which arenon-corresponding to the light-emitting element E3, represent mixturesof the specular light reflected from the supporting member (FIG. 12A)and the diffuse light reflected from the toner pattern (FIG. 12B).

It is clear from comparison of FIG. 12A with FIG. 12B, the distributionof the outputs of the light-receiving elements D1 to D5 when thedetection light is reflected from the surface of the supporting memberdiffers from the distribution when the detection light is reflected fromthe toner pattern. Therefore, the toner density of the toner pattern canbe calculated from data about the difference between those outputs.

However, from the viewpoint of simplicity of the algorism for thecalculation, it is preferable to calculate the toner density from dataexcluding the outputs of the light-receiving elements representing themixtures of the specular reflection component reflected from thesupporting member and the diffuse reflection component reflected fromthe toner pattern.

In the toner-density measuring method according to the fourteenthembodiment, M-number of the light-emitting elements emit the detectionlight sequentially, and N-number of the light-receiving elements receivethe detection light. The output of the corresponding light-receivingelement is categorized to the specular reflection output, and theoutputs of the non-corresponding light-receiving elements arecategorized to the diffuse reflection output. Thus, the toner density iscalculated from those categorized outputs.

If the toner-density measuring method is put into the above case of thelight-emitting element Ei and the light-receiving element Di, where i isan arbitrary integer from 1 to 5, when the light-emitting element Eiemits the detection light, the light-receiving element Di, whichreceives only the specular reflection component of the detection lightfrom the light-emitting element Ei, is assumed as the light-receivingelement corresponding to the light-emitting element Ei, and the outputof the light-receiving element Di is categorized to the specularreflection output.

Moreover, the light-receiving elements Dj, where j≠i and j≠i±1, areassumed as the light-receiving elements non-corresponding to thelight-emitting element Ei, and the outputs of the light-receivingelements Dj are categorized to the diffuse reflection output.

When, for example, the light-emitting element E3 emits the detectionlight, the output of the light-receiving element D3, which iscorresponding to the light-emitting element E3 is the specularreflection output, and the outputs of the light-receiving elements D1and D5, which are non-corresponding to the light-emitting element E3,are the diffuse reflection output.

Because the light-receiving elements D2 and D4 receive both the specularreflection light and the diffuse reflection light, the outputs of thelight-receiving elements D2 and D4 are categorized to neither thespecular reflection output nor the diffuse reflection output.

In this manner, the outputs of the light-receiving elements D1 to D5 arecategorized into three types, i.e., the specular reflection output, thediffuse reflection output, and the output neither the specularreflection output nor the diffuse reflection output. If the tonerdensity is calculated from the specular reflection output and thediffuse reflection output only, the algorism for the calculation issimplified because the influence of the reflection from the surface ofthe supporting member is clearly differentiated from the influence ofthe reflection from the toner pattern.

An additional explanation is given for the case when the light-emittingelement E3 emits the detection light. In the output of thelight-receiving element D3, which is corresponding to the light-emittingelement E3, the entire output is the specular reflection output, i.e.,the diffuse reflection light is zero. In the outputs of thelight-receiving elements D1 and D5, which are non-corresponding to thelight-emitting element E3, the entire output is the diffuse reflectionoutput, i.e., the specular light reflected from the supporting memberare zero.

In most cases, the number of the light-receiving elements Dj, which arenon-corresponding to the light-emitting element Ei, is two or larger.Even if the diffuse light spreads over and two or more light-receivingelements receive the diffuse light, the correct diffuse reflectionoutput is obtained by calculating a sum of the outputs of thelight-receiving elements Dj. Thus, the diffuse reflection light isdetected more accurately.

For example, when the light-emitting element E3 emits the detectionlight to the toner pattern DP1, the output of the light-receivingelement D3 is the specular reflection output and the outputs of thelight-receiving elements D1 and D5 are the diffuse reflection outputrepresenting the diffuse light reflected from the toner pattern only. Ifthe sum of the outputs of the light-receiving elements D1 and D5 iscalculated and the calculated larger data is used as the diffusereflection output, the toner density is measured more accurately.

The toner density is calculated from the outputs of the threelight-receiving elements D1, D3, and D5 based on a difference betweenthe reflection property of the supporting member (the specularreflection output, i.e., the output of the light-receiving element D3)and the reflection property of the toner pattern (the diffuse reflectionoutput, i.e., the outputs of the light-receiving elements D1 and D5)(difference between the current specular reflection output and thereference specular reflection output and difference between the currentdiffuse reflection output and the reference diffuse reflection output).

The calculation is described briefly below.

It is calculated, by focusing only the specular reflection output as thereflection property, a correlation between the toner density of thetoner pattern and a difference between the output of the light-receivingelement D3 representing the detection light reflected from thesupporting member and the output of the light-receiving element D3representing the detection light reflected from the toner pattern.Alternatively, it is calculated, by focusing only the diffuse reflectionoutput as the reflection property, a correlation between the tonerdensity of the toner pattern and a difference between the sum of theoutputs of the light-receiving elements D1 and D5 representing thedetection light reflected from the supporting member (=0) and the sum ofthe outputs of the light-receiving elements D1 and D5 representing thedetection light reflected from the toner pattern. Thus, the tonerdensity is measured based on those correlations.

If both the specular reflection output and the diffuse reflection outputare focused, the toner density can be calculated more accurately. In theabove description, “difference” includes various meanings, of course,including “value obtained by a subtraction”.

The outputs of the two light-receiving elements D2 and D4, which are notcorresponding to the light-emitting element E3, are the mixtures of thespecular reflection output and the diffuse reflection output, andtherefore it is difficult to separate the influences of the tworeflection properties. To make the algorism for calculation simpler, thetoner density is calculated from data excluding the outputs of thoselight-receiving elements, which makes it possible to implement the moreefficient processing. In the above description, it is assumed that whenthe light-emitting element Ei emits the detection light to the surfaceof the transfer belt, the corresponding light-receiving element Di andthe adjacent light-receiving elements Dj (j=i±1) receive the reflecteddetection light as the specular light.

As described above, if a non-specular intermediate transfer belt or thelike is used as the supporting member, the detection light is diffuselyreflected even from the surface of the toner pattern.

However, if the reflection property of the light diffusely reflectedfrom the supporting member is different from the reflection property ofthe light diffusely reflected from the toner pattern, the distributionof the outputs of the plural light-receiving elements representing thelight diffusely reflected from the supporting member is different fromthe distribution representing the light diffusely reflected from thetoner pattern. Therefore, the toner density can be measured from adifference between the distributions.

An example where the detection light is diffusely reflected from thesurface of the supporting member is described below.

In the example, both M, i.e., the number of the light-emitting elementsof the reflective optical sensor, and N, i.e., the number of thelight-receiving elements are seven.

The conditions in this example are almost the same as the conditions inthe example illustrated in FIGS. 3A to 3C except are the numbers of thelight-emitting elements and the light-receiving elements are seven, andthe supporting member is the non-specular intermediate transfer beltthat diffusely reflects the detection light.

To make the drawing simpler, a degree of diffusion of the detectionlight reflected from the toner pattern is assumed larger than a degreeof diffusion of the detection light reflected from the intermediatetransfer belt. If the degree of diffusion of the detection lightreflected from the toner pattern is smaller than the degree of diffusionof the detection light reflected from the intermediate transfer belt,the following description should be read with “intermediate transferbelt” and “toner pattern” switched.

FIG. 13A is a bar chart of the outputs of the light-receiving elementsD1 to D7 when the light-emitting element E4 emits the detection light tothe area out of the toner pattern (intermediate transfer belt).

The light-receiving elements D2 to D6 receive the specular light and thediffuse light reflected from the intermediate transfer belt. The outputsof the light-receiving elements D1 and D7 are zero.

FIG. 13B is a bar chart of the outputs of the light-receiving elementsD1 to D7 when the light-emitting element E4 emits the detection light tothe toner pattern.

It is clear from FIG. 13B that all of the light-receiving elements D1 toD7 receive at least one of the specular light and the diffuse lightreflected from the toner pattern.

Because the degree of diffusion of the detection light reflected fromthe toner pattern is larger than the degree of diffusion of thedetection light reflected from the intermediate transfer belt, thedistribution of the outputs illustrated in FIG. 13B is spreading morethan the distribution of the outputs illustrated in FIG. 13A.

It is necessary to identify, from among the outputs of thelight-receiving elements D2 to D6 that are larger than zero, an outputincluding the diffuse reflection output from the bar chart of FIG. 13A.The output of the light-receiving element D4 corresponding to thelight-emitting element E4 is, of course, the specular reflection output.

If it is assumed that the surface of the intermediate transfer belt isspecular, it is easy to identify the light-receiving elements inpositions to receive the specular reflection light through an opticalsimulation by using a modeled reflective optical sensor and anexperiment using the actual reflective optical sensor and the transferbelt with the specular surface.

If the light-receiving elements in positions to receive the specularreflection light are identified in prior, the outputs of thelight-receiving elements including the diffuse reflection light only areidentifiable from among the outputs of the light-receiving elements D2to D6 in FIG. 13A.

FIG. 13C is a bar chart illustrating, with hatching, the specularreflection output that is measured through the experiment using thetransfer belt having the specular surface.

As compared FIG. 13C with FIG. 13A, it is clear that the output of thelight-receiving element D4 illustrated in FIG. 13A is the specularreflection output representing the specular light reflected from theintermediate transfer belt, and the outputs of the light-receivingelements D2 and D6 are the diffuse reflection outputs representing thediffuse light reflected from the intermediate transfer belt.

As illustrated in FIG. 13A, the outputs of the light-receiving elementsD1 and D7 are zero. This means that the outputs representing the diffusereflection light are zero. The outputs of the light-receiving elementsD3 and D5 are the mixtures of the specular reflection output and thediffuse reflection output.

It means that, in the case illustrated in FIG. 13B, the output of thelight-receiving element D4 represents only the specular light reflectedfrom the toner pattern, and the outputs of the light-receiving elementsD1, D2, D6 and D7 represent only the diffuse light reflected from thetoner pattern. The outputs of the light-receiving elements D3 and D5 arethe mixtures of the specular reflection out and the diffuse reflectionout.

In other words, the output of the light-receiving element D4, whichcorresponds to the light-emitting element E4, is categorized to thespecular reflection output, and the outputs of the light-receivingelements D1, D2, D6 and D7, which are non-corresponding to thelight-emitting element E4, are categorized to the diffuse reflectionoutput.

The outputs of the light-receiving elements D3 and D5 are not used forthe calculation for the toner density, because they are the mixtures ofthe specular reflection component and the diffuse reflection component.

The two cases are described above: one is described with reference toFIGS. 12A and 12B where M=N=5 and the transfer belt with the specularsurface that is assumed to specularly reflect the detection light isused, and the other is described with reference to FIGS. 13A to 13Cwhere M=N=7 and the intermediate transfer belt with the non-specularsurface that is assumed to diffusely reflect the detection light isused. Those cases are exemplary, and therefore M and N can be changed tosome other values and some other types of the supporting member can beused.

As illustrated in FIGS. 12A to 12B and 13A to 13C, if only thelight-receiving element Di and the adjacent light-receiving element Di±1are in positions to receive, when the light-emitting element Ei emitsthe detection light, the specular reflection light, the outputs of theadjacent light-receiving element Di±1 are the mixtures of the specularreflection output and the diffuse reflection output.

In this case, the number of the light-receiving elements that are inpositions to receive the diffuse reflection light is N−3 (or N−2 whenany of the light-emitting elements on both ends emits the detectionlight). It means that even if the diameter of the spot of the detectionlight reflected from the supporting member is larger than the pitch ofthe light-receiving elements because of, for example, usage of thelight-emitting elements and the light-receiving elements arranged at asmall pitch, only the light-receiving element Di and the adjacentlight-receiving element Di±1 receive the specular light reflected fromthe supporting member, and therefore the number of the light-receivingelements that outputs the diffuse reflection output is at the maximum.Thus, the efficiency of detecting the diffuse reflection light isimproved.

Although M is equal to N in the above cases, M can be unequal to N.Corresponding relation between the light-emitting elements and thelight-receiving elements in other cases where M is unequal to N isdescribed with reference to FIGS. 6A to 6C.

In the example illustrated in FIG. 6A, N is 15 and M is 30. Thelight-receiving element Di is corresponding to the light-emittingelements E1 i and E1 i.

In the example illustrated in FIG. 6B, M is 15 and N is 30. Thelight-emitting element Ei is corresponding to the light-receivingelements D1 i and D2 i.

In the example illustrated in FIG. 6C, there are arranged the sevenlight-emitting elements E1, . . . , Ei, . . . , an E7 and the 14light-receiving elements D1, . . . , Di, . . . , an D14. Thelight-emitting element Ei is corresponding to the light-receivingelements Dj and Dj+1, where j=2i−1.

The toner-pattern positional detection is described below, where M isequal to N, and the light-receiving elements Di and Dj, where j=i±1, arepositions to receive, when the light-emitting element Ei emits thedetection light to the supporting member, the specular light. In thefollowing example, the light-emitting elements E1 to EM, where M is 100,are aligned at a 100-μm pitch in the main-direction. That is, thearrangement length is 10 mm.

The light-receiving elements D1 to DN, where N is 100, are aligned at a100-μm pitch in the main-direction. The size of the spot falling on thesurface of the supporting member when the light-emitting element Ei,where i is an arbitrary integer from 1 to 100, emits the detection lightis 80 μm. The width of the toner pattern in the main-direction is equalto the pitch of the light-emitting elements, i.e., 100 μm.

When the light-emitting element Ei emits the detection light, thedetection light is specularly reflected from the supporting member, andis received by the light-receiving elements Di and Dj (j=i±1). Thechange in the output of each of the light-receiving elements D1 to D100is checked while the light-emitting elements E1 to E100 turn ON/OFFsequentially. If the outputs of the light-receiving element Di and Di+1(specular reflection outputs) are low when the light-emitting elementsEi and Ei+1 are ON, it is determined that the toner pattern is betweenthe light-emitting elements Ei and Ei+1 in the main-direction.

In other words, the position of the toner pattern having the width of100 μm in the main-direction is detected accurately by unit of 100 μm orlower.

A reflective optical sensor device according to a fifteenth embodimentof the present invention is described with reference to FIG. 14.

The reflective optical sensor device includes a reflective opticalsensor 141 and a processing unit 142. The reflective optical sensor 141can be any one of the reflective optical sensors illustrated in FIGS.3A, 4A, 4B, 6A, 6B, 6C, 7A, 7B, etc.

The processing unit 142 categorizes the outputs of the reflectiveoptical sensor 141. More particularly, the processing unit 142categorizes, in the described above manner, the output of thelight-receiving element corresponding to the light-emitting element inthe ON state to the specular reflection output, and the output of thelight-receiving element non-corresponding to the light-emitting elementin the ON state to the diffuse reflection output.

According to an aspect of the present invention, there are provided amethod of measuring a toner density in a novel manner, a reflectiveoptical sensor and a reflective optical sensor device that are used inthe method, an image forming apparatus that performs the method by usingthe reflective optical sensor and the reflective optical sensor device.

Because the toner density is measured for a short time, an operatingefficiency of a main activity, i.e., image formation is improved.Moreover, an amount of toner to be consumed for the toner pattern issuppressed.

According to another aspect of the present invention, the image formingapparatus forms at least one of a mono-color image or a multi-colorimage, and calculates the toner density of each color.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. A position detection method of detecting aposition of a detection target on a supporting member that moves in apredetermined direction, the position detection method comprising:emitting a detection light onto the supporting member with alight-emitting unit; receiving a reflected light reflected from at leastone of the supporting member and the detection target with alight-receiving unit; detecting a position of the detection target basedon a difference between a reflection property of the supporting memberto the detection light and a reflection property of the detection targetto the detection light, wherein the light-emitting unit includes Mnumber of light-emitting elements aligned in a direction that isinclined to a direction that is perpendicular to the predetermineddirection, where M is equal to or larger than three, and thelight-receiving unit includes N number of light-receiving elementsaligned in a single direction, where N is equal to or larger than three,and wherein the detecting of the position of the detection target isperformed based on output from the light-receiving elements.
 2. Theposition detection method according to claim 1, wherein the detectingincludes when a first light-emitting element emits the detection light,categorizing an output of a first light-receiving element correspondingto the first light-emitting element to a specular reflection outputrepresenting specular reflection light, and categorizing outputs ofnon-corresponding light-receiving elements to the first light-emittingelement to diffuse reflection outputs representing diffuse reflectionlight; and detecting a position of the detection target based oncategorized outputs of the light-receiving elements.
 3. A positiondetection method of detecting a position of a toner pattern on asupporting member, the toner pattern being formed on the supportingmember that moves in a predetermined direction in an image formingmethod, the position detection method comprising: emitting a detectionlight onto the supporting member with a light-emitting unit; receiving areflected light reflected from at least one of the supporting member andthe toner pattern with a light-receiving unit; detecting a position ofthe toner pattern based on a difference between a reflection property ofthe supporting member to the detection light and a reflection propertyof the toner pattern to the detection light, wherein the light-emittingunit includes M number of light-emitting elements aligned in a directionthat is inclined to a direction that is perpendicular to thepredetermined direction, where M is equal to or larger than three, andthe light-receiving unit includes N number of light-receiving elementsaligned in a single direction, where N is equal to or larger than three,and wherein the detecting of the position of the toner pattern isperformed based on output from the light-receiving elements.
 4. Theposition detection method according to claim 3, wherein the tonerpattern is a position detecting pattern including line patterns eachperpendicular to the predetermined direction and line patterns each notperpendicular to the predetermined direction, and the emitting includesemitting the detection light sequentially from the light-emittingelements within a scanning time in which the position detecting patternpasses through an area to be exposed to the detection light in thesub-direction.
 5. The position detection method according to claim 3,wherein the toner pattern is a position detecting pattern including linepatterns each perpendicular to the predetermined direction and linepatterns each not perpendicular to the predetermined direction, and thelight-emitting unit and the light-receiving unit include P number oflight-emitting/light-receiving groups each including m number of thelight-emitting elements and n number of the light-receiving elements,where P is equal to or larger than two and m and n are equal to orlarger than three, the light-emitting/light-receiving groups arearranged in a direction that is parallel to or inclined to the directionthat is perpendicular to the predetermined direction, and the emittingincludes emitting the detection light within a scanning time in whichthe toner pattern passes through an area to be exposed to the detectionlight in the predetermined direction in such a manner that m sets of Pnumber of light-emitting elements that are selected from differentlight-emitting/light-receiving groups are turned ON/OFF one set afteranother set, the P number of light-emitting elements of each set beingturned ON/OFF simultaneously.
 6. A position detection sensor thatdetects a position of a detection target on a supporting member thatmoves in a predetermined direction, the position detection methodcomprising: a light-emitting unit that emits a detection light onto thesupporting member, and a light-receiving unit that receives a reflectedlight reflected from at least one of the supporting member and thedetection target, wherein the light-emitting unit includes M number oflight-emitting elements aligned in a direction that is inclined to adirection that is perpendicular to the predetermined direction, where Mis equal to or larger than three, and the light-receiving unit includesN number of light-receiving elements aligned in a single direction,where N is equal to or larger than three, and wherein the positiondetection sensor is configured to detect the position of the detectiontarget based on output from the light-receiving elements.
 7. Theposition detection sensor according to claim 6, wherein the direction inwhich the light-emitting elements are aligned and the direction in whichthe light-receiving elements are aligned are inclined to the directionthat is perpendicular to the predetermined direction, at a predeterminedangle that is determined based on a velocity of movement of thesupporting member in the predetermined direction when the reflectiveoptical sensor is in a position to detect a position.
 8. The positiondetection sensor according to claim 6, wherein the light-emittingelements are aligned in a plurality of first lines, the first linesbeing displaced from each other in the predetermined direction, thelight-receiving elements are aligned in a plurality of second lines, thesecond lines being displaced from each other in the predetermineddirection, and a distance between adjacent first lines and a distancebetween adjacent second lines in the predetermined direction are setbased on a velocity of movement of the supporting member in thepredetermined direction when the reflective optical sensor is in aposition to detect a position.
 9. The position detection sensoraccording to claim 6, wherein the light-emitting unit and thelight-receiving unit include P number of light-emitting/light-receivinggroups each including m number of the light-emitting elements and nnumber of the light-receiving elements, where P is equal to or largerthan two and m and n are equal to or larger than three, thelight-emitting/light-receiving groups are arranged on one or more lines,and when detecting a position, m sets of P number of light-emittingelements that are selected from different light-emitting/light-receivinggroups are turned ON/OFF one set after another set, the P number oflight-emitting elements of each set being turned ON/OFF simultaneously.10. The position detection sensor according to claim 6, wherein onelight-emitting element corresponds to at least two light-receivingelements.
 11. The position detection sensor according to claim 6,wherein one light-receiving element corresponds to at least twolight-emitting elements.
 12. The position detection sensor according toclaim 6, further comprising at least one of: an illumination opticalsystem that guides the detection light from the light-emitting elementstoward the surface of the supporting member in a convergent manner; anda light-receiving optical system that guides the reflected lightreflected from the surface of the supporting member toward thelight-receiving unit in a convergent manner.
 13. The position detectionmethod according to claim 1, wherein the light emitting unit forms aplurality of light spots as the detection light on the supportingmember, and the position of the detection target is detected based on adifference between (1) a reflection property of the supporting member tothe plurality of light spots and (2) a reflection property of thedetection target to the plurality of light spots.
 14. The positiondetection method according to claim 3, wherein the light emitting unitforms a plurality of light spots as the detection light on thesupporting member, and the position of the toner pattern is detectedbased on a difference between (1) a reflection property of thesupporting member to the plurality of light spots and (2) a reflectionproperty of the toner pattern to the plurality of light spots.
 15. Theposition detection sensor according to claim 6, wherein the lightemitting unit forms a plurality of light spots as the detection light onthe supporting member, and the position of the detection target isdetected based on a difference between (1) a reflection property of thesupporting member to the plurality of light spots and (2) a reflectionproperty of the detection target to the plurality of light spots.